


Mingling Primaries

by SansyFansySkele (SakuraSkeletonz)



Category: Undertale (Video Game)
Genre: Dom Sans, Ecto-Tongue, Ectobiology, M/M, No real specific timeline or route, Sub UF!Sans, They're in the Undertale Universe though, Undertale Sans/Underfell Sans, dubcon, selfcest
Language: English
Status: Completed
Published: 2016-03-16
Updated: 2016-03-16
Packaged: 2018-05-27 00:53:24
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,726
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6263071
Author URL: https://archiveofourown.org/users/SakuraSkeletonz/pseuds/SansyFansySkele
Summary: <blockquote class="userstuff">
              <p>What happens when Sans trys to get another version of himself to open up only for it to turn into something more?</p>
            </blockquote>





	Mingling Primaries

**Author's Note:**

> I don’t know but some how the Sans’ end up in the same universe, don’t ask, basically, inspired and at least partially based off [this post](http://singingsans.tumblr.com/post/137595031132/kinda-based-off-of-a-similar-experience-i-had-a) by @singingsans on tumblr.
> 
> Don't ask how Sans has a bowl in this one and not my other fic, I don't even know why. Haha.  
> Also, UF!Sans might not be the same as how most other portray him, and there IS a reason for that.
> 
> This turned into 9 and 1/2 pages on google docs and I don't know how it did... It wasn't supposed to be this long.

Sans walked into his house, it was a few weeks into the new reset and it was still strange to see the other version of himself sitting in the living room. No matter how often he walked in on the other, he always seemed to jump at least a bit, it was strange to see a mirror of himself who was so jumpy and always appeared to be on edge. They had a hard time talking, for the most part, stemming from what he assumed was the huge departure from the other’s normal universe. However, today Sans seemed more determined than ever to get the other to open up at least a bit, so he shuffled inside and shut the door, walking over to the sofa and hoping on.

He inhaled before looking at the other, “Look bud, I get that you aren’t really a talker, at least not about your world, but c’mon… You gotta open up at least a bit, we’re gonna be stuck like this until the next reset, I know you’re more than aware of that, so come on, you can talk to me… I’m you, after all.”

“Ugh, I _hate_ this stupid prying shit that everyone tries to pull, it ain’t gonna work on me, pal.” The other grumbled, looking to the side and crossing his arms, almost like he was pouting, wait...was he? He was!

Without being able to hold back a chuckle Sans shook his head, “Okay, look, I get where you’re from is obviously different, but you’re acting like such a child right now, come on, how old are you, 12?”

That seemed to lighten the mood, even if it was just a smidge because the other Sans looked over at him and smiled slightly, damn did those teeth look menacing, “Nah, I’m actually 22.”

Sans seemed taken aback for a moment, looking at the other in confusion before shaking it off, “Coulda fooled me with that pouty face you just made. God, just like what Pap would do…”

“H-heh, y-yeah, Pap…” That seemed to make the other look away, he seemed very worried again, his hands toying with the lining of his jacket, “I-I hope nothing bad is happening to him…” His eye seemed to flare at the thought, jumping from the couch, “I-I have to-”

“Bud, he’s not here…” Sans sighed, watching the other him almost deflate, it was agonizing to watch this guy, “But, while we’re on the subject of Pap, you said you were 22, right? How old is your bro then, like, 18 or something?” The other whirled around, red eye seeming to widen in surprise, that was it, this guy’s name was now Red, even if he protested Sans wasn’t backing down.

“N-nah, he’s actually 26.” Red said, now it was his turn to watch Sans get confused, that look was priceless, if he had to say something about it, “Why? Is your bro 18?”

“Heheh…” Sans shook his head, “Nope, Pap’s 22 and I’m 26.”

They seemed to stare each other down, the silence between them rather awkward, before it was broken by the younger, “Wow, no way…”

“Heh, yep, I’m the older bro in this house.”

“I don’t believe that.” Red said, looking at the other, “You’ve gotta be like me, c'mon, don’t lie.” Oh jeez, he sounded upset.

“Uh, no bud, I’m older. Pap has been my little bro our whole lives.”

That only seemed to frustrate the other all the more, causing him to stamp his foot, “Great, so I’m the youngest no matter what.”

“Hey, hey, calm down there, don’t throw a temper tantrum, red might be your color but it doesn’t suit you like this.” Sans said, waving his hand slightly.

“What’s that supposed to mean?” He huffed.

“You need to take a hint from Snowdin and _chill out_.”

Red stared at him in disbelief, was this guy really making jokes? How could he make jokes?! This wasn’t right! Why wasn’t he on edge? His mouth must have been hung open in astonishment, because the other only laughed.

“Did that render you speechless? Because I thought it was worth a few words.”

“H-how can you do that?” The other questioned, watching the older version of himself closely.

“Do what?”

“Make jokes like that? Be so lighthearted?! Aren’t you scared of being dusted?!”

That seemed to startle Sans, his one socket lighting with color as he watched the other closely, sure he worried about death sometimes but it was a lot less of a worry now-a-days. What was this other Sans’ deal? His face held surprise and he was unable to reply before the other went on.

“By people besides the kid? You know, like Undyne, or Alphys, or Asgore, or Toriel, or Grillby, or-”

Sans cut him short, “No, I’m not, why would I be scared of them hurting me?” His voice oozed confusion, that much was clear even to himself as the other looked at him with a look of what appeared to be dismay.

“H-how? How are you not scared of everyone here?! They could knock you down in one hit and you’d be dust, gone, just like that! Yet here you are, making jokes and being all comfortable and just... _talking_!”

It took him a minute to process what the other was saying, but his brain slowly put two and two together, his usual calm demure changed as he frowned, rubbing his temples, “Red, we have a lot to talk about.” He said solemnly.

The other seemed confused at the nickname, “Uh...wait, what? What did ya call me?”

Sans looked up, watching the other, “I called you Red, it’s something to distinguish us when I talk to you since it’s kinda weird to use your own name, it’s because of your magic… If it makes you feel more comfortable, feel free to call me Blue, I mean… It’s the same as my magic color.”

“Blue…” Red nodded in agreement as he said it before shaking his head, “Wait, you want me to talk about my home..? Yea, I don’t think that’s such a good idea…”

“Look, Red, it’ll help you if you talk to me.” Blue said, watching the other closely, almost like he was trying to read him.

Red grumbled, looking away and shifting awkwardly, “You aren’t scared of anyone but the kid then, huh…?”

Blue shook his head, sitting back, “Nah, which begs the question, why are you? I mean, I want to say your life is a lot harder than mine, but what exactly is your world like?”

“...The mantra we live by is “kill or be killed”...” Red moved, sitting down on the floor and brought his knees up to his chest, “And that’s not just something that’s used a scare tactic, it’s basically what everyone lives by… Except Pap and I…”

The blue magic user sat up, watching the other closely, “So...you and Pap have a good relationship?”

“Yea, Pap is the only one who cares about me, but… No one can know, or they’d use it against us, to kill us…”

 

“...So, Undyne and your bro aren’t friends?” He jumped as the other’s head snapped up, watching his soul beating fast.

“Fuck no! That bitch tried to _kill_ me multiple times saying it would be a mercy killing! I was a kid!” Red’s eye flared as he looked at the other, almost like he was going to call out an attack.

“Okay, okay, woah, calm down there bud…” The other replied, rubbing his skull, “So...she thinks it’s okay to kill anyone just because, or…?”

“It’s because I have 1HP, it’s because when she met us we were heading home and I ended up crying and running away and she tried to kill me and Pap had to protect me and kept saying that-”

“Woah, okay, you don’t have to keep talking about her, it’s okay… I think I understand why you didn’t want to open up… You could use some stress release, I bet.”

Red tilted his head, blinking, “What...do you mean?”

“Have you ever...well, smoked before?”

“W-well, Gerson smokes, but I’ve never… Well… I’ve never tried it.”

“You really could use it, hold on bud, I’ll be right back.” Blue said, standing up and stretching before heading up to his room, Red watching him closely, seeming rather curious.

It took a few minutes, and Red heard a lot of rustling as the other moved things around his room, but eventually Blue emerged carrying a small bag and what looked like a pipe, as well as… A lighter? He must have looked incredibly confused because Blue chuckled and said, “This will help, trust me. It’s called pot, it can help relieve stress. Not in the healthiest way, but it’s better than nothing, not like it’ll hurt us any.”

To that Red only nodded, still seeming rather anxious as Blue filled, what he assumed to be a pipe with some of the bundled leaves, “Uh...what’s that thing? It looks different from Gerson’s…”

“It’s called a bowl, at least that’s what I’ve heard it be called. I had one on the surface the first time I got up there, but I managed to find one in the dump after the first reset.”

“Oh… If this stuff is good for stress relief, why would people throw stuff related to it away?”

Blue shrugged, “It’s not exactly legal everywhere on the surface, I guess people just do it to stay safe? I dunno.” The other nodded, watching as Blue moved it over to him once it was lit, “Here, do you want the first hit?”

Red shook his head, “Uh, I don’t know if I should.”

“Hmmm, lets see how you feel after some of it is in your system.”

“How would it get there without me doing anything?”

“Heh, trust me bud, in a few minutes it’ll fill the room.” Blue chuckled, moving the bowl to his own mouth and opening it, pulling in some of the smoke and holding in a few moments before breathing it out.

After a while, the entire lower floor of the house was full of smoke and Red was swaying, Blue watching and chuckled, “Here, I have an idea.”

“Huh..? What is it..?” Red questioned, tilting his head slightly as Blue took another hit and got closer, blowing the smoke into the younger one’s face, his face was already slightly flushed and his head was swimming. The younger moved their faces closer, confusing the elder a moment before he felt the teeth click together, only to feel the other’s conjured tongue press against his teeth.

Blue realized what was happening, having already placed everything down a moment prior, he moved opened his teeth once more, wrapping his arms around Red. His tongue was conjured as well, pulling the younger version of himself into a kiss, as they both pulled each other into an embrace. A few moments passed before they pulled back, Red laughing slightly.

“You are so high dude.” Blue chuckled, drool being wiped from his chin.

“Shut the fuck up.” The other laughed more, wiping the drool from his own chin.

It took a few moments before they both ended up looking into eachother’s eyes, Red had his white pupils, which was a surprise for Blue to see, causing his cheekbones to deepen in color, watching him closely, thinking what he wanted to ask over, “Red..?”

“Y-yeah, Blue?”

“You look really cute like that, you know.”

“L-like what?”

“You’re pupils, you’re not draining your magic.”

“O-oh, y-yeah.” The younger’s blush darkened, averting his gaze as he watched giggled slightly, “Y-you know, u-uh…”

“You don’t have to open up about everything, okay?”

“W-what? O-oh, okay. I just…”

“Mmm, thinking about your bro again?”

Red nodded slightly, looking back up at the other, seeing something in his sockets that looked like a fire, “Y-yea, I’m just really worried about him.”

“Heh, same here, but uh… I get the feeling it’s a little more than just being worried.” Blue smirked slightly, which only caused Red to avert his gaze once more.

“N-no, I’m just really worried is all… I mean, Pap is all I have back home and-”

“Buddy, I can see you getting shy about this subject, so I’ll lighten the mood a bit, how about it?”

“L-lighten it how, exactly?”

Blue moved one hand down, pressing it against the top of the other’s shorts, which earned him a gasp, “You’re obviously thinking about Papyrus, aren’t you?”

“U-uh, n-no, why would I be thinking about my b-bro that way?”

Shaking his head Blue moved forward, kissing the other’s neck, “If you aren’t thinking about him, then what are you thinking about? I know this stuff can fog your mind up, but you’ve gotta be thinking about _something_ , don’t leave me hanging.”

Red let out a shaky gasp before feeling the other nibbling his cervical vertebrae, which made him shudder, “O-okay, look, m-maybe I’m just a little curious, o-okay?”

“Curious about what?” He looked up at the other.

“F-fuck, curious about having sex with someone? I mean, it’s not like I haven’t...well, you know, done anything to myself but still…”

“I guess I could give you what you need.”

“W-wait, are you serious?”

“Well, yea, I mean, it’s no _skin off my nose_.”

Red snorted slightly, before feeling the other pressing his hand against his growing erection, “F-fuck.”

“I mean, you need to give me the okay first.” Blue mused, watching Red closely.

“S-shit, yes, please.” Red replied, looking away from the other shyly.

“You have to look me in the eyes and tell me what you want.” The older of the two said, sounding rather forceful.

A shiver travelled up the younger skeleton’s spine before he turned his head, locking eyes with the other once more, now he knew what he’d seen in the elder’s sockets… Fire, the fire of lust, if he had the ability, he probably would have been gulping right now, shit did the other version of him look hot, “I-I want you to fuck me.” He said quietly.

“Oh? What was that?” Blue cocked his head slightly, still keep his eyes locked on the other’s, palming the other through his shorts, causing him to hiss slightly.

“F-fuck me.” He said a little louder.

“I don’t think I heard you right.” The other smirked, pressing them closer together, barely giving the younger any more friction.

“F-fuck, goddamn it..! I want you to fucking wreck me!” Red broke, his entire face burning red in shame as he felt the other pull away.

“Now was that so hard to say?” Blue teased him.

“F-fuck you, Blue.” The other sputtered out, looking to the side before he heard the other shifting, he watched closely as the other skeleton removed his clothing slowly, starting with his jacket and then the white sweater underneath before stopping.

“I get the feeling you could stare all day, but you might want to get those pesky clothes off too, if you want to get anywhere.”

At that Red felt like his face was completely lit ablaze, removing his own jacket and sweater before stopping at his shorts, already having kicked his shoes off before this whole ordeal started, “W-well, who goes first here then?”

“Well, I say you should, I mean, you’re the one who wants it, right~?”

Red felt a rather shy suddenly, “L-like the blue glow emitting from your pelvis says you don’t.”

Blue shrugged, “True enough, I guess. How about you play along with me though, pet..~?”

The younger’s sockets went completely dark a moment before one flared red, his entire body suddenly felt like it was burning in that moment and he didn’t understand why, this was a feeling he wasn’t use to. His hands moved shakily, dropping his shorts as he watched the other, his face could be a good replacement ambient lighting at the moment, or that’s what he was telling himself because it sure felt like if they turned the lights off his face would make up for the darkness. He gasped as his cock sprung free, however; he felt chilled on a different part of his pelvis, that was… strange, to say the least, what exactly had the other done to him?

Blue smirked, pulling his own shorts off and letting his own cock free, “Well, I guess we’re the same size, not that it’s a huge surprise.” He chuckled, moving over and wrapping on of his hands around the other’s cock, “So, you want to have some fun, huh~?”

“Y-yes, please.” He begged, watching the other before he felt Blue starting to move his hand, causing him to gasp, it was different to have someone else touching him, but it was also odd because it almost felt the same as when he masturbated… Red chalked that up to it _literally being another version of himself_. Almost off of instinct one of his own hands moved to the other’s cock, starting to jerk him off as well.

“H-hah, that’s not bad for the first time touching someone else, huh?” Blue chuckled, moving his own hand faster, causing Red to moan.

“B-Blue, f-fuck, k-kiss me..?” He whined slightly, which surprised the other a bit before he nodded, complying to the request. Their tongues met once more, right above their throbbing cocks, Red was pretty sure if it wasn’t from the fog in his mind he’d be dead from embarrassment. He honestly isn’t sure when the other moved his hand behind his hips, but he’s aware that there’s something being teased, causing him to moan and pull from the kiss, drool trickling down his chin, tongue hanging out, “F-fuck…”

“Wow, I hadn’t realized you’d conjured up a pussy as well..~” Blue cooed, it sounded like praise to the other, which only caused his spine to arch slightly, “Hmm, I think I know what to do.”

Red whined when he felt the other move his hands, watching him closely, “W-what do you mean, B-Blue?”

“Oh, you’ll see. I think you should get on the couch for now, it’ll be a lot nicer than the floor, I think.”

Without really asking what the other met, Red moved over, laying back on the couch before Blue got on top of him, smirking, “A-alright, so what’s happening now? I, uh… Like I said, this _is_ my first time.”

“You probably won’t believe me, but honestly, it’s mine too.” Blue chuckled.

“You’re pulling my leg.”

“No, I’m actually telling the truth. Honestly it’s my first time with someone else as well.”

“I still don’t believe you.” Red said.

Blue only shrugged before leaning back, “Okay, Red, we’re going to do something that should be enjoyable for both of us.”

“And what’s that?”

“It’s called a 69.”

“W-wait, really?”

“Yeah, besides, it’ll be good.” Blue moved, get on top of the other so his cock was in front of Red’s face, licking the other’s cock, teasing his pussy as well, causing Red to gasp before he moved up, licking the other’s cock back. Smirking, Blue moved two fingers into Red, causing the other to moan under him, taking his cock into his mouth as well.

“A-ahh, B-Blue, m-mmm…” Red shuddered, looking up at the the other’s pelvis a moment before moving forward, taking the other into his own mouth, suck on his cock. His mind was swimming, perhaps the fog probably made it feel all the more pleasureable, but he didn’t care what the reason was it just felt to amazing… That’s why when the other pulled away he let out a frustrated noise before letting go of the cock in his mouth, “B-Blue, what the fuck…”

“I think we should get to the main event now, huh?” Blue smirked over his shoulder, which caused Red’s legs to feel weak, guess it was a good thing he wasn’t standing. His mouth felt very dry all of the sudden, eyes focused on the other as he switched positions again, their eyes locking once more.

“Okay, this time this is more than serious, Red… You’re technically giving yourself to me completely, you know that, right?” Red could only nod slowly, “Then I want you to give me a serious answer and I want it before we do anything else… Do you really want to do this?”

“Y-yes, I do, Blue.”

“Are you sure?”

“Y-yes, goddamn it, please!” Red cried out in frustration, which startled the elder a bit before he laughed, “I-I get that you’re concerned, but fuck, I just… I just want you to fuck me, okay?”

“Okay, if you’re really sure.” Blue said, and before the other could have another outburst he’d started to move forward, pressing into him. Red moaned, gripping onto the couch as he watched the other closely, seeing the pleasure on his face.

“B-Blue, h-holy fucking shit..!” Once the other was fully inside, Red panted, his tongue hanging out as he looked at the other.

“Heh, that’s a nice look on you, Red.”

“S-shut it…” The other whined slightly before feeling a rough thrust, gasping.

“Heh, let’s get started then.” Red watched the other, moaning as he started to thrust, his pussy throbbing and clenching around the other’s cock.

“A-ahh, B-Blue~” The younger moaned out, his arms moving up and wrapping around his arms around the other, bringing him down into a sloppy kiss. They were both moaning and panting, Red’s cock twitching between them.

Blue smirked, moving one hand down and stroking the other, causing him to moan louder, pulling from the kiss, his face screwing up in pure pleasure, “D-damn, that looks so hot.” The elder groaned, thrusting more, feeling Red clench around him, “I-I’m gonna cum~”

“O-okay~ P-please do~ I-I’m close too~”

Blue’s hips continued snapping forward for a few more thrusts before forcing in and releasing inside the other, his blue cum shoot out as Red squirt and his ropes of red ectoplasm shot up onto his ribs, where Blue’s freehand travelled to. He gently ran his fingers over each rib, smirking at the small shudders and gasps Red was making until the other whined, “T-to much, Blue, t-to much... ”

“Heh… Guess I know where to start next time..~”

That only made Red sink into the couch slightly, a small mewl of acknowledgement leaving him, what had he gotten himself into this time?


End file.
